CVE-2021-39878Public exploitNetwork attack vector

Cross-site scripting via unchecked Jira return link

Published Oct 5, 2021 · Updated Aug 4, 2024

Cross-site scripting in GitLab 13.0 through 14.1.6, 14.2.0 through 14.2.4, and 14.3.0 allows remote authenticated users to run JavaScript. JiraConnect::UsersController assigns the unvalidated return_to parameter to a link, and external_link emits it without restricting the URL scheme. Exploitation requires a logged-in Safari user to click the crafted link on an instance without CSP; the script then runs in that user's GitLab origin.

CVSS severity5.8
Medium
EPSS probability0.80%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Cross-site scripting in GitLab 13.0 through 14.1.6, 14.2.0 through 14.2.4, and 14.3.0 allows remote authenticated users to run JavaScript. JiraConnect::UsersController assigns the unvalidated return_to parameter to a link, and external_link emits it without restricting the URL scheme. Exploitation requires a logged-in Safari user to click the crafted link on an instance without CSP; the script then runs in that user's GitLab origin.

The record

CVE
CVE-2021-39878
Published
Oct 5, 2021
Updated
Aug 4, 2024
Vendor
GitLab
Product
GitLab
Classifications
CWE-79, T1204.001
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Oct 5, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=>=13.0, <14.1.7
  2. Affected versionversion=>=14.2, <14.2.5
  3. Affected versionversion=>=14.3, <14.3.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

GitLab · GitLabversion=>=13.0, <14.1.7; version=>=14.2, <14.2.5; version=>=14.3, <14.3.1

Published CVSS scores

3.5NIST NVDAV:N/AC:M/Au:S/C:N/I:P/A:N
5.4NIST NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
5.8GitLab Inc.CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:C/C:H/I:N/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1204.001User Execution: Malicious Link

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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